We propose to extend and develop our studies of the structural role of cholesterol and its fatty acid esters in membranes and atherosclerotic lesions. The proposed studies fall in three broad areas. (1) The biosynthesis of perdeuterated cholesterol will be abandoned in favor of chemical synthesis perhaps using new techniues of catalytic exchange in thin films. (2) Some of the neutron experiments will be carried out by using perdeuterated phospholipids rather than perdeuterated cholesterol. (3) Work will be done during the next year to characterize the disposition of cholesteryl esters in lipid bilayers by exploiting the large difference in scattering density between the deuterated phospholipid and the hydrogenated cholesteryl ester.